Does an English appeal court ruling increase the risks of miscarriages of justice when complex DNA profiles are searched against the national DNA database?

For very serious crimes, reporting scientists often have to contend with complex cases where literally hundreds of items are submitted by investigators for analysis. In order to efficiently expedite the challenge of comparing reference profiles to evidence profiles, many of which are mixtures, we have developed an investigative open source expert system CaseSolver. We have analysed a real case based on GlobalFiler involving 119 evidence profiles and 3 reference profiles. To provide a demonstration of the power of the system we also added the three references to a fictive large database of 1 million individuals in order to test subsequent recovery of the presumed true contributors. CaseSolver was used on a Fusion 6C validation study involving 25 two-to four-person mixture profiles based on 14 reference profiles. The sequential use of simple allele comparison, the qualitative model (forensim) and the quantitative model (EuroForMix) makes the analysis very fast and accurate-and finally, the software generates a list of potential match candidates which can be exported as a report. From these two studies we found that the resolution of match candidates from CaseSolver was the same as that reported by a scientist who worked manually through the samples, except that CaseSolver highlighted two manual errors. For the validation study we found low template DNA samples giving negative results, which demonstrate the limitations of the tool; but overall our assessment shows that CaseSolver will benefit all analyses involving mixture interpretation and screening. Importantly, CaseSolver removes the very time-consuming aspect of manual comparison and gives improved quality by preventing manual errors.

Section: The Performance Of Searching Large National Dna Databasessupporting

confidence: 88%

Section: Performance Of Database Searchmentioning

confidence: 99%

CaseSolver: An investigative open source expert system based on EuroForMix

Bleka

Prieto

Gill

2019

“…Non-contributor (nc) tests are carried out by replacing each suspect (S) in turn with a large number of random (R 1..N ) profiles [27] to generate a new LR nc per random profile. For simple proposition pairs (Table 2), how often a LR nc = x or more is accommodated by Pr(LR nc >x|Hd) <= 1/x, so we expect less than N/x 'matches', where there are N comparisons [28] and the mean LR avg =1 under Turing's expectation [26]. For complex proposition pairs shown in Table 2, how often LR nc >x occurs is accommodated by Pr(LR nc >x|Hd) <= LR Sa /x, where LR Sa is the LR produced using propositions where the known contributor in the numerator is S a .…”

Section: Our Role As Investigatormentioning

confidence: 95%

DNA commission of the International society for forensic genetics: Assessing the value of forensic biological evidence - Guidelines highlighting the importance of propositions

Gill

Hicks

Butler

et al. 2018

The interpretation of evidence continues to be one of the biggest challenges facing the forensic community. This is the first of two papers intended to provide advice on difficult aspects of evaluation and in particular on the formulation of propositions. The scientist has a dual role: investigator (crime-focused), where often there is no suspect available and a database search may be required; evaluator (suspect-focused), where the strength of evidence is assessed in the context of the case. In investigative mode, generally the aim is to produce leads regarding the source of the DNA. Sub-source level propositions will be adequate to help identify potential suspects who can be further investigated by the authorities. Once in evaluative mode, given the defence version of events of the person of interest, it may become necessary to consider alternatives that go beyond the source of the DNA (i.e., to consider activity level propositions). In the evaluation phase, it is crucial that formulation of propositions allows the assessment of all the results that will help with the issue at hand. Propositions should therefore be precise (indication of the number of contributors, information on the relevant population etc.), be about causes, not effects (e.g. a 'matching' DNA profile) and to avoid bias, must not be findings-led. This means that ideally, propositions should be decided based on the case information and before the results of the comparisons are known. This paper primarily reflects upon what has been coined as "sub-source level propositions". These are restricted to the evaluation of the DNA profiles themselves, and help answer the issue regarding the source of the DNA. It is to be emphasised that likelihood ratios given sub-source level propositions cannot be carried over to a different level - for example, activity level propositions, where the DNA evidence is put into the context of the alleged activities. This would be highly misleading and could give rise to miscarriages of justice; this will be discussed in a second paper. The value of forensic results depends not only on propositions, but also on the type of results (e.g. allelic designations, peak heights, replicates) and upon the model used: it is therefore important to discuss these aspects. Finally, since communication is key to help understanding by courts, we will explore how to convey the value of the results and explain the importance of avoiding the practice of transposing the conditional.

“…The fourth option is practised, but can be criticised, notably regarding the justification and disclosure of bases of experience (for an example, see the case R v Dlugosz [99] and a criticism [100], of the testimony in the case). More generally, it is relevant to mention here that the notion of 'personal probability' should not be understood as an arbitrary or speculative assertion.…”

Section: Assigning Probabilities For Key Factors When Propositions Ofmentioning

confidence: 99%

Evaluation of forensic genetics findings given activity level propositions: A review

Taylor

Kokshoorn

Biedermann

2018

104

The evaluation of results of forensic genetic analyses given activity level propositions is an emerging discipline in forensic genetics. Although it is a topic with a long history, it has never been considered to be such a critically important topic for the field, as today. With the increasing sensitivity of analysis techniques, and advances in data interpretation using probabilistic models ('probabilistic genotyping'), there is an increasing demand on forensic biologists to share specialised knowledge to help recipients of expert information address mode and timing of transfer and persistence of traces in court. Scientists thereby have a critical role in the assessment of their findings in the context of the case. This helps the judiciary with activity level inferences in a balanced, robust and transparent way, when based on (1) proper case assessment and interpretation respecting the hierarchy of propositions (supported by, for example, the use of Bayesian networks as graphical models), (2) use of appropriate data to inform probabilities, and (3) reporting guidelines by international bodies. This critical review of current literature shows that with certain prerequisites for training and quality assurance, there is a solid foundation for evidence interpretation when propositions of interest are at the 'activity level'.